<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>作业</title>
    <style>
        #header{
            width: 400px;
            height: 700px;
            background-color: red;
            margin: 30px auto;   
            position: relative;       
        }
        #header>div{
            height: 60px;
            width: 400px;
            position: absolute;
            bottom: 0px;
            background-color: green;
        }
        input{
            margin-left: 10px;
            margin-top: 10px;
            width: 310px;
            height: 30px;
        }
        button{
            height: 40px;
            width: 60px;
        }
    </style>
</head>
<body>
    <div id="header">
        <div>
            <input type="text">
            <button>发送</button>
        </div>
    </div>
</body>
</html>